11... b8d7  12. a2a4 After this move White has a comfortable advantage, so Black's previous play needs to be improved. The problem here is the space advantage, the lack of counterplay, and the king being in danger because the white knight has an inviting square on g5. White's last move aims to exchange the bishop with Ba3, since after all the white bishop is limited by the pawn chain. 12... f8b4  13. c1a3  13... a6a5 